Photographic silver halide emulsion supersensitized with a benzimidazole base



Aug. 2 8, 1951 B. H. CARROLL ETAL 2,566,167

PHOTOGRAPHIC SILVER HALIDE EMULSION SUPERSENSITIZED Y WITH A BENZIMIDAZOLE BASE v Filed April 20, 1946 50H7' H. CARROLL JHN SPE/VCE INVENToRs 7PM-PM rheterocyclic nitrogen bases.

Patented Aug. 28, -199.51

PHOTOGRAPHIC SILVER HALIDE EMULSION SUPERSENSITIZED WITH A BENZIMIDA- ZOLE' BASE Burt H. Carroll and John Spence, Rochester, N. Y., assignors to Eastman Kodak Company, lRochester, N.' Y., a corporation of New Jersey Application April 20, 1946, Serial No. 663,763

This invention relates to sensitized photographic emulsions and to a process for preparing the same. This application is a continuationin-part of our copending application Serial No. 466,796, led November 24, 1942 (now United States Patent 2,398,778, dated April 23, 1946).

It is known that the spectral distribution of spectral sensitivity of certain spectrally sensitized emulsions can be altered and an increase of sensitivity obtained in some spectral region, by incorporating certain additional sensitizing dyes in the spectrally sensitized emulsions. (See United States Patent 2,158,882, dated May 16, 1939, and 2,159,565, dated May 23, 1939.) The eilect thus produced has come to be known as supersensitization. Supersensitization of certain spectrally sensitized emulsions can also be effected by incorporating certain substantially colorless heterocyclic bases, viz. those containing an amino group, in the spectrally sensitized emulsions. (See United States Patent 2,177,635, dated October 31, 1939.) Supersensitization diiers from hypersensitization which involves treatment of finished lms or plates, an operation which normally reduces the pAg and increases the pH of the emulsion, with consequent decreased stability.

We have now found a new method for supersensitizing spectrally sensitized emulsions, which not, only does not reduce the stability of the emulsions, but is especially valuable as a means of giving good panclromatic sensitized emulsions oi' high speed and good color balance.

It is, accordingly, an object of our invention to provide new supersensitized photographic emulsions. A further object is to provide a process for preparing such emulsions. Other objects will become apparent hereinafter.

In accordance with the invention, a photographic silver halide emulsion other than a chloride emulsion, e. g. silver chlorobromide (which may contain small amounts of silver iodide), silver bromide or silver bromiodide emulsions, spectrally sensitized with a (at least one) cyanine dye is supersensitized by incorporating in the emulsion one or more benzimidazole bases. Our invention is Vdirected principally to emulsions of such grain size that the emulsions give a substantially neutral-toned image in Eastman Kodak Companys D-76 developer, and should not be confused with prior proposals to obtain blueblack tones in line-grain emulsions by means of Moreover, our invention involves incorporation of the benzimidazole bases in the emulsion before exposure of the emulsion and should not be confused with 10 Claims. (Cl. 95--7) proposals to develop with color-forming developers silver salt images, in the presence of certain heterocyclic nitrogen bases which contain a reactive methyl group.

The benzimidazole bases advantageously employed in practicing our invention are of a specinc type and can be defined as benzimidazole (benziminazole) bases selected from the group consisting of benzimidazole and benzimidazole containing a substituent (i. e. at least one substituent) selected from the group consisting of alkyl groups, alkoxyl groups, hydroxyalkyl groups, aryl groups, aryloxyl groups, alkylmercapto groups, arylmercapto groups, acyl groups, acyloxyl groups and halogen atoms. Examples of such substituents are: methyl, ethyl, methoxyl, ethoxyl, hydroxyethyl, phenyl, phenoxyl, ,methylmercaptd ethylmercapto, phenylmercapto, acetyl, propionyl, benzoyl, acetoxyl (acetoxy), propionoxyl (propionoxy) and benzoxy groups, and chlorine, bromine and iodine atoms. i

Exemplary of the benzimidazole bases advantageously employed in practicing our invention are benzimidazole which has the following formula:

etc.

The majority of cyanine dyes which are supersensitized by the benzimidazole bases are charterized by the fact that the dyes produce two types of sensitization depending upon conditions. Such diierent types of sensitization are described by Leermakers, Carroll and Staud, J. Chem. Physics 5, 878 (1937), and by Schwarz, Sci. et Ind. Phot. 10, 233 (1939). When a cyanine dye of this type is used as a sensitizer in low concentration, it exhibits a sensitizing maximum displaced about 20 to 50 mu. toward the red from the absorption maximum in ethyl alcohol solution. On increasing the concentration of the dye, or upon digesting the emulsion containing the dye in the lower concentration, or both, a second maximum of sensitization develops` at longer wavelengths, which may be accompanied by 'an increase in total optical sensitization. In some cases, a decrease in sensitivity at the first maximum can be detected. These phenomena are consistent with the hypothesis of two states of the sensitizing dye in an equilibrium which is controlled by concentration. The benzimidazole bases fayor the formation of a second maximum which occasionally is appreciably displaced from the normal second maximum. The increase in sensitivity apparently corresponds to increased conversion of the dye to the state Corresponding to the second maximum of sensitization. In some cases, the eiect appears to correspond to a more complete conversion than has ever been obtained without a supersensitizer, Vand in any c ase the long Wavelength sensitivity is better than can be obtained from the same concentration or" dye without the benzimidazole base.

The following are exemplary of the cyanine dyes which are supersensitized in accordance with our invention:-

3lrdiethyl-6'-rnethoXy-2'-cyanine iodide. 3,3-diethyl-Q-methylthiacarbocyanine bromide. 9-ethyl-3,3'-dimethylthiacarbocyanine bromide. 5ch1oro3,3,9-triethylthiacarbocyanine iodide. 5,5 -dichloro3,3 ,9 -triethylthiacarbocyanine iodide. 35,3 -diethyl-9-methyl-4,5,4 ,5 -dibenzothiacarbo cyanine bromide. 3,3-diethyl-Q-methylselenathiacarbocyanine bromide.

5' chloro-3,3-diethyl-9-methy1selenathiacarbocyanine iodide. 3,3 d iethyl 9 methylselenacarbocyanine bronine bromide. 3,1 -diethyl-B' -methoxythia-:Z -cyanine bromide. 11diethyl- 2,2 'cyanine bromide. 1, 1'-diethyl-2,2-carbocyanine bromide. 9-ethyl-3,1 -dimethylthia-2' -carbocyanine iodide. 3,3' -diethyl-9-methyl--phenyloxathiacarbocyanine iodide. 3,3diethyloxatricarbocyanine iodide.

The sensitizing dyes can be employed in -any desired concentration. Ordinarily from l0 to 30 mg. of dye per liter of emulsion will suiiice to produce the optimum sensitizing effect. The methods of incorporating sensitizing dyes in emulsions are well known'to those skilled in the art. Ordinarily it is preferable to `dissolve the dye in a water-miscible solvent, such as methanol or ethanol, beforeillorporating in the emulsion. One or more sensitizihg dyes can be employed.

The amount of benzimidazole base employed is not critical. Usually the full supersensitizing effect is developed at a concentration of 0.10 to 1.5 grams per liter of emulsion. At these concentrations practically none of the benzimidazole bases has an appreciable eiect on the pH of the emulsion. The benzimidazole bases can be added to the emulsions with, before or after the sensitivzing Clye or dyes. More than one benzimidazole base can be employed. The benzimidazole bases are preferably, but not necessarily, diluted with a water-miscible, solvent, such as methanol, before incorporation in the emulsions. The sensitizing dye or dyes and the benzimidazole. base or bases 'Call be added to the emulsions at any convenient stage of their preparation, but preferably to the washed, finished emulsions before coating.

The following examples will serve to illustrate further the results obtained in accordance with Qur invention.

benzimidazole Red Minus Blue (g- .pcrliterof i emulsmn') )Speed Gamma Speed Gamma none 10.6 3. 91 29.0 3 65 0. 58 16. 5 3. 91 4?). 5 4. 4.0

Example 2 A fast negative gelatino'-silver-bromiodide developing-out emulsion was sensitized with 3,3"- diethyl-9-methylselenacarbocyanine bromide (20 mg. per liter of emulsion) and to a portion of the spectrally sensitized emulsion was added 2- methylbenzimidazole. A portion of the spectrally sensitized emulsion without the Z-methylbenzimidazole and a portion containing it were exposed through red (Wratten No. 25) and minus blue (Wratten No. 12) iilters. The results are tabulated below:

Z-methylbenzi- Red Minus Blue midazole (g. per liter of emulsion) Speed Gamma Speed Gamma none l. 42 600 l. 5l 0.25 290 1.26 860 1.47

Some of the benzimidazole bases, While eiiecting an increase of sensitivity (Speed) in some spectral region, cause a decrease in others, and must be employed with that fact in mind.

The accompanying drawing illustrates graphically the supersensitizing eiect obtained with two` of our new combinations in a gelatino-silverbromiodide emulsion. Each ligure in the drawing is a diagrammatic reproduction of two spectrograms. In Fig. l, Curve A represents the sensitivity ofl a gelatine-silver-bromiodide emulsion containing 3,3-dietnyl-Q-methylselenacarbocyanine bromide in a concentration of 20 mg. per liter of emulsion. Curve B represents the Sensitivity of the saine emulsion containing 3,3 diethyl-9-methylselenacarbocyanine bromide in a concentration of about 20 mg. lper liter of emulsion and containing, in addition, benzimidazole in a concentration of about 0.58 g. per liter of emulsion. It will be observed that with the benzimidazole in the emulsion, a new sharp maximum appears at about 640 ma and the red speed is considerably increased. In Fig. 2, Curve C represents the sensitivity of a gelatinosilver-bromiodide emulsion containing4 3,3diethyl-Q-methylselenacarbocyanine bromide in a `concentration of 20 mg. per liter ofy emulsion. Curve D represents the sensitivity oi the same emulsion containing 3,3-diethyl-9-methylselenacarbocyanine bromide in a concentration of about 20 mg. per liter of emulsion and containing, in addition, Z-methylbenzimidazole in a concentration of about 0.25 g. per liter of emulsion. f It will be observed that the maximum of `sensitivity is shifted toabout 610 mit,

Our invention is primarily directed to the customarily employed gelatino-silver-halide developing-out emulsions, such as gelatina-silverchlorobromide, gelatino-silver-bromi-de and gelatino silver bromiodide developing out emulsions, especially emulsions for development to black-and-White images by means of non-colorforming developers, e. g. hydroquinone-N-methylp-amino-phenol developers.

Emulsions prepared in accordance with our invention can be coated in the usual manner upon any desired support, such as cellulose nitrate support, cellulose acetate support, polyvinyl acetal resin support, metal support, glass support or paper support.

Cyanine dyes are des-cribed and defined, e. g. in The Theory of the Photographic Process, by C. E. K. Mees, The MacMillan Company, New York, 1942.

What we claim as our invention and desire to be secured by Letters Patent of the United States is:

l. A photographic silver halide emulsion selected from the group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions spectrally sensitized with av sensitizing cyanine dye and containing, as a supersensitizer, a benzimidazole base selected from the group consisting of benzimidazole and benzimidazole containing a substituent selected from the group consisting of halogen atoms, alkyl groups, alkoxyl groups, hydroxyalkyl groups, aryl groups containing only carbon and hydrogen atoms, aryloxyl groups in which the aryl portion contains only carbon and hydrogen atoms, alkylmercapto groups, arylmercapto groups in which the aryl portion contains only carbon and hydrogen atoms, acyl groups containing only carbon and hydrogen atoms plus one oxygen atom, and acyloxyl groups containing only carbon and hydrogen atoms plus two oxygen atoms.

2. A photographic gelatino-silver-halide developing-out emulsion selected from the group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions spectrally sensitized with a sensitizing cyanine dye and containing, as a supersensitizer, a benzimidazole base selected from the group consisting of benzimidazole and benzimidazole containing a substituent selected from the group consisting of halogen atoms, alkyl groups, alkoxyl groups, hydroxyalkyl groups, aryl groups containing only carbon and hydrogen atoms, aryloxyl groups in which the aryl portion contains only carbon and hydrogen atoms, alkylmercapto groups, arylmercapto groups in which the aryl portion contains only carbon and hydrogen atoms, acyl groups containing only carbon and hydrogen atoms plus one oxygen atom, and acyloxyl groups containing only carbon and hydrogen atoms plus two oxygen atoms.

3. A photographic gelatino-silver-halide developing-out emulsion selected from the' group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions spectrally sensitized with a sensitizing cyanine dye and containing, as a supersensitizer, 2-methylbenzimidazole which has the formula:

C-GHa 4. A photographic gewann-Silverman@ developing-out emulsion selected from the group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions spectrally sensitized with a sensitizing cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a second maximum of sensitivity at a wavelength longer than that of the-first maximum, the emulsion containing, as a supersensitizer, a benzimidazole base selected from the group consisting of benzimidazole and benzimidazole containing a substituent selected from the group consisting of halogen atoms, alkyl groups, alkoxyl groups, hydroxyalkyl groups, aryl groups containing only carbon and hydrogen atoms, aryloxyl groups in which the aryl portion contains only carbon and hydrogen atoms, alkylmercapto groups, arylmercapto groups in which the aryl portion contains only carbon and hydrogen atoms, acyl groups containing only carbon and hydrogen atoms plus one oxygen atom, and acyloxyl groups containing only carbon and hydrogen atoms plus two oxygen atoms.

5. A photographic gelatino-silver-halide developing-out emulsion selected from the group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions spectrally sensitized with a sensitizing cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion -containing the dye at the lower concentration, produces a maximum of sensitivity at a wavelength longer than that of the rst maximum, the emulsion containing, as :a supersensitizer, benzimidazole having the formula:

\CH N/ 6. A photographic gelatino-silver-bromiodide developing-out emulsion spectrally sensitized with a sensitizing cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration produces a maximum of sensitivity at a Wavelength longer than that of the iirst maximum, the emulsion containing as a supersensitizer, a benzimidazole base selected from the group consisting of benzimidazole and benzimidazole containing a substituent selected from the group consisting of halogen atoms, alkyl groups, alkoxyl groups, hydroxyalkyl groups, aryl groups containing only carbon and hydrogen atoms, aryloxyl groups in which the aryl portion contains only carbon and hydrogen atoms, alkylmercapto groups, arylmercapto groups in which the aryl portion contains only carbon and hydrogen atoms, acyl groups containing only carbon and hydrogen atoms plus one oxygen atom, and acyloxyl groups containing only carbon and hydrogen atoms plus two oxygen atoms.

'7. A photographic gelatino-silver-bromiodide developing-out emulsion spectrally sensitized with a sensitizing dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration produces a maximum of sensitivity at a wavelength longer than that of the rst maximum, the emulsion co'ntaining, as a supersensitizer, benzimidazole having the formula:

a maximum of sensitivity at a wavelength longer 20 than that of the rst maximum, the emulsion containing, as a supersensitizer, Z-methylbenzimid'az'ole having the formula:

9. A photographic gelatino-silver-halide developing-out emulsion selected from the group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions spectrally sensitized with a sensitizing cyanine dye and containing, as a supersensitizer, benzimidazole which has the formula;

\CH \N/ 10. A photographic gelatino-silver-halide developingout emulsion selected from the group consisting of silver chlorobromide, silver bromide and silver bromiodide developing-out emulsions s pectrally sensitized with a sensitizing cyanine dye which produces a maximum of spectral sensitivity in the emulsion at one concentration and at a higher concentration, or upon digestion of the emulsion containing the dye at the lower concentration, produces a maximum of sensitivity at a wavelength longer than that of the irst `Ii'aximufn, the emulsion containing, as a supersens't'izer, 2-mthylben`zimidazole having the formula:

BURT H. CARROLL. JOHN SPENCE.

REFERENCES CITED The following references are of record in the file of this patent: i

UNITED STATES PATENT Number Name Date 2,066,099 Dieterle Dec. 29, 1936 2,158,882 Mees May 16, 1939 2,296,306 Peterson Sept. 22, 1942 2,353,754 Peterson July 18, 1941i 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION SELECTED FROM THE GROUP CONSISTING OF SILVER CHLOROBROMIDE, SILVER BROMIDE AND SILVER BROMIODIDE DEVELOPING-OUT EMULSIONS SPECTRALLY SENSITIZED WITH A SENSITIZING CYANINE DYE AND CONTAINING, AS A SUPERSENSITIZER, A BENZIMIDAZOLE BASE SELECTED FROM THE GROUP CONSISTING OF BENZIMIDAZOLE AND BENZIMIDAZOLE CONTAINING A SUBSTITUENT SELECTED FROM THE GROUP CONSISTING OF HALOGEN ATOMS, ALKYL GROUPS, ALKOXYL GROUPS, HYDROXYLAKYL GROUPS, ARYL GROUPS CONTAINING ONLY CARBON AND HYDROGEN ATOMS, ARYLOXYL GROUPS IN WHICH THE ARYL PORTION CONTAINS ONLY CARBON AND HYDROGEN ATOMS, ALKYLMERCAPTO GROUPS, ARYLMERCAPTO GROUPS IN WHICH THE ARYL PORTION CONTAINS ONLY CARBON AND HYDROGEN ATOMS, ACYL GROUPS CONTAINING ONLY CARBON AND HYDROGEN ATOMS PLUS ONE OXYGEN ATOM, AND ACYLOXYL GROUPS CONTAINING ONLY CARBON AND HYDROGEN ATOMS PLUS TWO OXYGEN ATOMS. 